Industrial trucks of this type mostly have a driving wheel driven by an electric motor and idling load-carrying wheels. It is known to associate brakes with both the driving wheel and load-carrying wheels. The brake for the driving wheel can also be associated directly with the driving motor. It is known to employ hydraulic drum brakes for the brakes described. It is also known to use single-disc spring force loaded magnetic brakes for the driving motors. Those are mostly designed as so-called “fail-safe” brakes because there is a prescription that if an electric steering, as is frequently used for such industrial trucks, fails the vehicle requires to be slowed down in a regular manner.
For industrial trucks provided with three-phase motors, it is also known to be slowed down by means of the driving motor that acts as a generator. The braking action produced by means of the generator may help in realizing a “coast-down brake” as is disclosed in DE 196 29 386 C1, for example. This state of the art also describes the use of target value ramps in dependence on the position of the brake pedal.
EP 0 908 348 has made known to use the help of the driving motor to achieve a load-independent braking behavior. An identical braking distance which is proportional to the excursion of the brake pedal is predetermined for a speed control of the driving motor. Speed target value ramps are predetermined which are chosen depending on the pedal position. Brakes of the load-carrying wheels which are also provided in the known case are connected from a certain pedal position onwards.
EP 0 814 051 B1 has made known to provide at least one brakable axle and at least one non-brakable axle for an industrial truck with a control unit generating a variable control signal setting the admissible maximum speed of the industrial truck. The control signal is varied by means of the control unit in dependence on the direction of travel of the industrial truck in such a way that a higher maximum speed is allowed during a travel in the direction of the brakable axle than is during a travel in the direction of the non-brakable axle.
EP 0 758 591 A1 has made known to generate an electric braking signal by means of a braking signal generator which is actuated by the brake signal. The brake signal is supplied to the motor control which predetermines the extent of energy recovery. What results therefrom is the extent of generative deceleration. Since the braking torque produced by the motor is frequently insufficient to ensure the desired deceleration a delay sensor is provided which measures the delay in deceleration and generates a signal for a braking system which produces a mechanical braking force in response to the deficiency of motor-induced deceleration in order that the braking behavior be attained.
It is the object of the invention to provide a braking system for an industrial truck by means of which a low-wear braking effect can be achieved. The object is attained by the features of claim 1. The braking behavior is intended to be approximated to that of a hydraulic brake.